Nationally, gas prices now average $3.61 a gallon. That's a 12-cent drop from early March and 33 cents below $3.94 a year ago. / Joe Raedle, Getty Images

by Gary Strauss, USA TODAY

by Gary Strauss, USA TODAY

At a time when gas prices traditionally rise, they continue to slide, even as the nation heads into peak summer driving season.

Nationally, prices now average $3.61 a gallon. That's a 12-cent drop from early March and 33 cents below $3.94 a year ago, when prices were close to a 2012 peak. And despite record-high averages in February, motorists paid an average $3.54 a gallon in the first quarter, vs. $3.58 in the first quarter of 2012.

Consumers in some regions of the Rocky Mountains - close to relatively cheap North American crude oil near refiners - are filling up on sub-$3-a-gallon gas. In Montana, which averages $3.37 a gallon, prices in some cities, such as Great Falls, are in the $2.90s. Casper and Cheyenne, Wyo., had average prices below $3 for the entire quarter.

"We'll probably see more markets with $3-a-gallon gas next week,'' says Tom Kloza, chief oil analyst at the Oil Price Information Service and GasBuddy. Among the likely areas: South Carolina, Tennessee and Georgia.

GasBuddy analyst Patrick DeHaan estimates that each penny per gallon saved means savings of about $108 million a day over year-ago prices. The price-tracking Internet app tracks prices at more than 140,000 gas stations.

Crude oil prices continue to slide. Benchmark West Texas Intermediate crude fell to a two-week low of $92.70 a barrel Friday, ending the week down nearly 5%. Meanwhile, the Energy Information Administration says U.S. inventories were at a 22-year high last week.

Still, prices at the pump could be prone to spikes - as they did last year when refinery disruptions caused supply issues in California and the Midwest. But DeHaan and Kloza expect continued price weakness for the next few weeks.

"The coast is not yet clear for a 2013 top, but it was always nonsense to suggest that prices might vary from $4.25 to $5 a gallon,'' Kloza says. "That won't happen unless there is a disruption in the Mideast."

And despite the year-over-year price drop, there is still pain at the pump, based on historical trends. During 2009's first quarter, gas averaged less than $1.90 a gallon and averaged less than $1.60 a gallon in the first quarter of 2003.

Highest current prices in the continental U.S.: California, averaging $4.03, vs. $4.28 a year ago. Price ranges in some markets have never been wider. GasBuddy says drivers in Washington, D.C., can save $1.14 a gallon shopping for the cheapest price available.